A major complication of cancer chemotherapy, of antiviral chemotherapy, or of exposure to ionizing radiation is damage to bone marrow cells or suppression of their function. Specifically, chemotherapy and exposure to ionizing radiation damage or destroy hematopoietic progenitor cells, primarily found in the bone marrow and spleen, impairing the production of new blood cells (granulocytes, lymphocytes, erythrocytes, monocytes, platelets, etc.). Treatment of cancer patients with cyclophosphamide or 5-fluorouracil, for example, destroys leukocytes (lymphocytes and/or granulocytes), and can result in enhanced susceptibility of the patients to infection. Many cancer patients die of infection or other consequences of hematopoietic failure subsequent to chemotherapy or radiation therapy. Chemotherapeutic agents can also result in subnormal formation of platelets which produces a propensity toward hemorrhage.
Similarly, mustard gas poisoning results in damage to the hematopoietic system, leaving one more susceptible to infection. Inhibition of erythrocyte production can result in anemia. Failure of the surviving bone marrow stem cells to proliferate and differentiate rapidly enough to replenish leukocyte populations results in the inability of the body to resist pathogenic infectious organisms. Various disease states, such as neutropenia, including idiopathic forms, are also related to impairment of specific components of the hematopoietic system.
Compounds which improve or aid in the restoration of hematopoiesis after bone marrow damage or suppression caused by chemicals, radiation, disease, or other pathological conditions associated with deficient hematopoiesis, are useful as therapeutic and prophylactic agents.
Several polypeptide hematopoietic growth factors (produced primarily through recombinant DNA technology) are known. These hematopoietic growth factors, which include erythropoietin (EPO), the interleukins (especially Interleukin-1, Interleukin-3, and Interleukin-6) and the colony-stimulating factors (such as granulocyte colony-stimulating factor, granulocyte/macrophage colony-stimulating factor, or stem-cell colony-stimulating factor), have been reported to have some utility in improving hematopoiesis. Some agents broadly characterized as "biological response modifiers" (BRM's) can also enhance some indices of hematopoiesis. BRM's which modify hematopoiesis include agents like bacterial endotoxin, double-stranded RNA, azimexone, glucans and other yeast and bacterial polysaccharides, dextran sulfate, maleic acid divinyl ether polyanion (MVE2), and tumor necrosis factor.
D. W. Bennett and A. N. Drury, J. Physiol. 72:288 (1931) disclosed that the administration of 100 mg of guanosine to rabbits by intraperitoneal injection resulted in an intense decline in leukocyte counts. Initial levels of leukocyte counts were 7700 per mm.sup.3, but after administration of guanosine, the leukocyte counts declined to only 500 to 1000 per mm.sup.3. After 10 hours, and for 24 hours thereafter, there was leukocytosis (11,000 per mm.sup.3).
D. G. Wright, Blood 69:334-337 (1987) reported the effect of guanosine and guanine on cultures of a specific human myeloid leukemia cell line (HL-60). The conversion of immature blast cells into mature granulocytes in vitro was reported to be induced by various chemical agents (including retinoic acid, dimethylformamide and tiazofurin). Incubation of HL-60 cells with guanine or guanosine prevented their induced maturation into functional neutrophils; incubation with inosine had no effect on induced maturation.
A. K. Oshita, et al., Blood 49:585-591 (1977) suggested that cyclic nucleotides (e.g., 3',5'-cylic adenosine monophosphate (cAMP) or 3',5'-cyclic guanosine monophosphate (cGMP)) may participate in the regulation of cell proliferation. In mouse bone marrow cells in culture, cGMP produced an increase in the number of colonies formed under stimulatory influence of serum taken from endotoxin-treated mice. cGMP had no effect in the absence of post-endotoxin serum. 5'-guanosine monophosphate and cAMP were inactive.
Beljanski et al., Cancer Treat. Rep. 67:611-619 (1983) disclosed that partial hydrolysis of E. coli ribosomal RNA yields short (approximately 40 bases) oligonucleotides that have some demonstrable leukopoietic activity in rabbits treated with cyclophosphamide. The authors proposed that the oligonucleotides were acting as replication primers for DNA synthesis in bone marrow cells. They also disclosed that the polyribonucleotides polyguanosine monophosphate, polyadenosine monophosphate, and a copolymer of adenine and guanine nucleotides failed to stimulate leukocyte formation.
T. Sugahara et al., Brookhaven Symposia in Biology:284-302 (1968) reported that yeast RNA hydrolysate, mixtures of adenosine, cytidine, guanosine, uridine, and their corresponding 3'-ribonucleoside monophosphates did not improve survival after acute lethal doses of ionizing radiation. The compounds improved survival of mice when administered periodically during repeated exposure to sublethal doses of gamma irradiation. The authors stated that the treatment agents were not improving proliferation or differentiation of surviving stem cells, but were apparently prolonging the survival of damaged mature cells. The hydrolysate, the ribonucleosides, and the ribonucleoside monophosphates all decreased the numbers of nucleated cells and hematopoietic cell colonies (colony-forming units) in spleen and bone marrow (the major sites of hematopoiesis) compared to irradiated untreated control mice.
Goodman et al. (U.S. Pat. Nos. 4,539,205, 4,849,411, and 4,643,992) disclose the use of aldosyl guanine derivatives having substituents having an electron-withdrawing effect greater than hydrogen in the 8 position of the guanine moiety, for modulating immune response.
Some acyl derivatives of oxypurine nucleosides have been synthesized for use as protected intermediates in the synthesis of oligonucleotides or analogs of nucleosides or nucleotides. See Sigma Chemical Company 1991 catalog, pages 1702-1704.
W. A. Fleming and T. A. McNeill, J. Cell. Physiol. 88:323-330 (1976) reported that the nonionic surfactant compounds Polysorbate 80 and Saponin increase the responsiveness of bone marrow cells in culture to the influence of sub-optimal amounts of colony stimulating factors. The surfactants were active over a very narrow concentration range, with maximum activity at 10 ng/ml, and minimal activity at concentrations ten-fold greater or ten-fold lower. The effect of surfactants on hematopoiesis in viva was not examined.